Exemplary ball bearing retainers to be incorporated in a ball bearing include a crown-shaped retainer (snap cage), a machined retainer (machined cage) and a wave-shaped retainer (ribbon cage), which are each composed of a resin or a metal. Such a ball bearing retainer includes a ring-shaped body to be disposed between inner and outer races of the ball bearing, and a plurality of pocket surfaces provided on the body to define a plurality of pockets for retaining balls of the ball bearing, the pocket surfaces each having a concaved spherical shape similar to the shape of the ball of the ball bearing and having a curvature radius slightly greater than the curvature radius of the ball, and defining openings in an inner surface and an outer surface of the ring-shaped body.
The ball bearing incorporating the ball bearing retainer suffers from a problem such that noise is liable to occur particularly when a higher viscosity lubricant is used for improvement of the service life of the ball bearing or when the ball bearing is rotated at a higher speed. The cause of the noise is conceivably as follows. When the ball bearing is rotated, the balls revolve between a pair of races and, at the same time, are pressed against the ball bearing retainer in wide-area contact with the respective pocket surfaces of the ball bearing retainer with the intervention of thin films of the lubricant (more strictly in sliding contact because of the rotation of the balls).
In the thin lubricant films formed between the surfaces of the balls and the pocket surfaces, however, the lubricant is less fluid and may stagnate. The stagnant lubricant has a higher viscous resistance to increase a resistance to the sliding contact. As a result, the noise is generated during the rotation of the ball bearing. At the same time, the ball bearing suffers from problems of increase in torque and reduction of the service life of the lubricant due to temperature increase.
For prevention of these problems, it is proposed that a projection is provided on at least one of the pocket surfaces defining the respective pockets in the vicinity of an opening in one of the inner and outer surfaces of the ring-shaped body as projecting from the corresponding pocket surface inward of the pocket (see Patent Document 1).
Patent Document 1: Japanese Patent No. 3035766 (Claim 1, and Paragraph Nos. 0003 to 0005 and 0012)